Update KB2553248 for Microsoft Outlook 2010 was released in April 2012. After you install this public update, you may receive the following error message when you try to open an Information Rights Management (IRM)-protected message:
This build of Microsoft Office is unsigned and cannot be trusted by a production Windows Rights Management Services (RMS Server). Before using Information Rights Management (IRM) in this build, specify a test RMS server.
This problem is caused by specific shipped files that are codesigned by using a certificate that is configured incorrectly. In this case, the Outlook.exe file is codesigned by using the problematic certificate.
To resolve this issue, apply the update that is described in the following article in the Microsoft Knowledge Base:
2598318 Description of the Outlook 2010 hotfix package (Outlook-x-none.msp): April 24, 2012